text: Both (R,R)- and (S,S)-pseudoephedrine can be used as chiral auxiliaries. Pseudoephedrine is reacted with a carboxylic acid, acid anhydride, or acyl chloride to give the corresponding amide.
  The α-proton of the carbonyl compound is easily deprotonated by a non-nucleophilic base to give the enolate, which can further react. The configuration of the addition compound, such as with an alkyl halide, is directed by the methyl group. Thus, any addition product will be syn with the methyl and anti to the hydroxyl group. The pseudoephedrine chiral auxiliary is subsequently removed by cleaving the amide bond with an appropriate nucleophile.